A microdisplay display system uses an array of spatial light modulators (the microdisplay) to modulate light in order to display images on a display plane. The microdisplay can modulate light by reflectively altering the transmission path of the light or blocking the transmission path of the light. Microdisplay display systems have enabled the production of high quality display systems at a reasonable cost.
One widely used form of microdisplay is a digital micromirror device (DMD). A DMD is made up of an array of micromirrors that pivot along an axis depending upon an image being displayed. A single image can be divided into a number of bit planes, which when displayed sequentially, are integrated by the human eye into a single image. There are multiple bit planes for each color of light in the microdisplay display system. An individual micromirror can assume one of two states, ON or OFF. When a micromirror is in an ON state, the micromirror can reflect light from a light source onto the display plane, while when the micromirror is in an OFF state, the light is reflected away from the display plane. The combined effect of all the micromirrors in the microdisplay, in conjunction with sequentially colored light, produces images on the display plane.
FIGS. 1a and 1b illustrate two commonly used forms of micromirrors. The diagram shown in FIG. 1a illustrates what is commonly referred to as a yokeless micromirror 100 and the diagram shown in FIG. 1b illustrates a yoked micromirror 150. The yokeless micromirror 100 includes a mirror 105 that is attached to a hinge 110, with the entirety resting on a hinge support structure 115. The mirror 105 pivots about the hinge 110 based on image data of the image being displayed. The yoked micromirror 150, of FIG. 1b, also includes a mirror 155 that is attached to a yoke 160. The yoke 160 is attached to the hinge 165. Both the mirror 155 and the yoke 160 pivot about the hinge 165.
FIGS. 2a through 2d illustrate potential micromirror positions. When in normal operation, a micromirror 200 can be in one of two positions, a first position that corresponds to an ON position and a second position that corresponds to an OFF position. The diagram shown in FIG. 2a illustrates one of the two positions. When another bit plane is to be displayed, or when the micromirror is not in use (e.g., during the power down process or when the device is completely turned off), the micromirror can be commanded to move to a reset position (e.g., parked position). The diagram shown in FIG. 2b illustrates the reset or parked position. Once in the reset position, the micromirror can move to either the ON position or the OFF position depending on the value of the image data. The diagrams shown in FIGS. 2c and 2d illustrate the ON position and the OFF position, respectively.
As the micromirror (mirror) 105 moves, a torque is applied to the hinge 110 in the same direction as the movement of the micromirror 105. If the micromirror 105 is operated in such a way that the micromirror 105 predominantly moves towards one side (one position, either ON or OFF), an effect known as hinge memory can occur. Hinge memory can be the result of the migration of the hinge material. If allowed to persist for an extended amount of time, hinge memory can cause catastrophic failure of the micromirror 105. For example, in displaying an all black (or an all white) image, the micromirrors of the microdisplay will spend a vast majority of the time (e.g., greater than 95%) in a single position. Practical examples would include the superposition of a black box containing a close-caption text stream over the image in a television, or an information display panel with text on a dark background.
Accordingly, what is needed in the art is a hinge memory mitigation system and method, which is configured to address the aforementioned issues.